viscous fan - how it works + options

[garyinwestoz]

I noticed the fan blade (red) on my 80 528i auto had a noticeable wobble after I had removed and cleaned it up. It seems that the centre aluminium fixing plate has buckled a bit - not sure if I did that whilst cleaning or its part of the original viscous fan bolt tension, which I released when I disassembled the fan from the viscous clutch.



I have another fan (black) and clutch - off a 78', but its bearing seems to be stuck



So I have a good viscous clutch with a slightly buckeled fan and a good fan with a stuck viscous clutch bearing.

So my question is - Does a slight fan wobble matter?

If I remove the black fan from its viscous clutch - will it buckle.


In looking this up, I found a viscous fan explanation on youtube by a E38/e31 guy. - very interesting how it works

https://www.youtube.com/watch?v=RDuGsDUiXQw

He explains quite well the interaction of the thermostat - which I didnt know.

I read a previous thread about getting the updated viscous clutch - that allows the fan to be removed without having to remove the radiator.
FCP Euro have 2 listed
https://www.fcpeuro.com/products/bmw-fa ... 1521723027 @ 64.77
https://www.fcpeuro.com/products/bmw-fa ... 1521723027 @ 61.10

I read that these need a different mounting or pulley - where can they be got?

[528i-1981]

Hi Gary - yes, the water pump pulley bolt pattern is different for the spin-on fan clutch flange. You want the flange (p/n 11511277387) and the matching pulley (p/n 11511271423):

https://www.realoem.com/bmw/enUS/showpa ... 1511271423

I got mine from Faulkner here in the States and it cost US$83 for the pulley and around $50 for the flange. I may have bought the flange on eBay as I see they're NLA on Faulkner.

You'll also want the special wrench to hold the mount bolts so you can turn the big mounting bolt on the clutch to get the fan off in the future.

https://www.ecstuning.com/b-schwaben-pa ... 170sch01a/

Pricey project for what seems like a mundane upgrade, but I did this in April and it's paid for itself the two times I've taken the fan off since I installed it.

[garyinwestoz]

Hi Eric
thanks for the links to the suppliers

does it matter if a fan wobbles a little?

[528i-1981]

Gary - You're probably asking the exact wrong guy, because I'm so OCD about stuff like this, I would remedy it just because it would irk me. As I'm talking to a guy that spent upwards of 10 hours on his back steam cleaning the underside of his E12, we may have something in common in this regard.

But I suspect there may be good reasons to fix this apart from aesthetics. That is if the wobble persists at high speed. It sounds like you've diagnosed the wobble while manually rotating the fan, and it's possible that it could correct itself at high speed. But if you've "locked in" the warp of the metal plate it may not. Also, if you've changed your clutch, you can't be sure the wobble isn't there.

One reason to correct is that when you switch to the spin-on mounting, you may find as I did that the fan rides closer to the rad. A wobble, if it's pronounced enough, may be enough for the fan blades to contact the rad fins. At 2500 RPM, the unbalance (if it persists) will cause greater wobble. The forces involved can be large even though the unbalance is rather small.

Absent interference with the rad, I would be concerned about the life of your water pump bearing. What a wobble really does is make the true axis of rotation dynamically deviate from the mechanical axis, and that means a lateral force will be transmitted to the pulley, the flange and then to the pump bearing (in other words, a force in the plane of the fan). In the math for calculating this force, because the fan is at the end of the axis of rotation, it's the farthest from the bearing so that increases the force of the deflection. The mass of the pulley and flange is then recruited into the wobbling system, which also increases the force generated. And the high rotational speed is actually the real driver of the force generation (in the math, rotational speed is squared).

Sustained vibration forces like this over time are bad for bearings, so I would probably do what I could to correct it. That said, now that you'll have a spin-on fan, it will be easier to replace the water pump if you need to!

I don't think that removing the fan clutch would create a wobble in the fan, but I don't have any experience with this.

[Mike W.]

Removing the fan from the fan clutch should not warp it, so don't worry about that, but wobble is not good, it should be pretty straight. I have seen the bolt on fans seize before too, so it's not unusual.

The newer style also requires a different water pump so don't forget that part. The screw on of the hub screws onto the water pump directly. One key to being able to get the screw on off in the future is to make sure it's not loose when you start the engine and give it a little dab of lube when you assemble it. Oh yeah, remember it's left hand threads when you're taking it off, I had a bear of a time the first time I removed one since I didn't know which way it turned.

The newer style is thermostatic, or at least it's supposed to be, but they too can be problematic and don't seem to live as long as the early style which is not thermostatic, but rather it kind of disengages at a certain RPM. Exactly how that works I don't really know.

[528i-1981]

The newer style also requires a different water pump so don't forget that part.

I didn't know that, as I replaced my water pump at the same time as the flange and the fan/clutch. I'm glad I did now.

[garyinwestoz]

Well , I remove the black fan from the non- functioning clutch and installed it on my good viscous clutch . Its aluminium centre piece is really flat - ( the red one is not flat)

seem to spin nicely